The present invention relates to electronic countermeasure techniques and more particularly to electronic countermeasure techniques which stretch out and distort a return pulse beyond the range gate of enemy compression pulse search radars so that radars will no longer produce accurate echo indications.
Range Gate Walk Off as previously accomplished by operational ECM systems utilizes an r-f memory system. This memory system is basically composed of a traveling wave tube and a delay device. The input pulse as received from the enemy equipment being jammed is detected and is used to gate ON the r-f memory loop, this loop normally operating with a gain of more than one so that the gating ON of this loop will permit a build up of oscillations. Once turned on, oscillations will build up at a gain peak of the loop. However, by turning on the loop only a fraction of the time it takes to build up to this preferred oscillation, the input signal frequency that is applied to the loop will be repeated by recirculating through the delay line and reamplification by the traveling wave tube. This essentially produces a stretched r-f pulse in the output corresponding to each r-f pulse at the input.
For the purposes of explanation here, the delay and input pulse width are equal. Certainly, an input pulse width which varies frequency within the pulse could not be walked off in this manner because the leading edge of the signal that is returned through the delay media would not be at the same frequency as the trailing edge of the input pulse. The output stretched waveform would not be frequency continuous.
Another disadvantage of such a memory loop for a range deception use against a radar which utilizes pulse compression is that the pulse width and delay media requirements are not compatible. R-f delays of about 0.5 microseconds are presently available with reasonable attenuations.
The present invention overcomes the faults and shortcomings of the above prior art systems and will successfully walk off the range gate of a system such as one which utilizes pulse compression, a random pulse rate frequency, pulse-to-pulse frequency hopping, and monopulse technique for angle tracking. The present invention as will be disclosed hereinafter will have the following input-output characteristics:
______________________________________ Radio Frequency Input Signal Characteristics PRF: 216 PPS .+-. 10% random Pulsewidth: 27 us Linear In-Pulse Frequency Variation: 1 mc (either + or -) Pulse-to-Pulse Frequency Hop: .+-.100 mc random Frequency: 5600 - 5800 mcs Pulse Train Modulation: None Radio Frequency Output Signal Characteristics PRf: 216 PPS .+-. 10% random Pulsewidth: 27 us Linear In-Pulse Frequency Variation: 1 mc (either + or -) Pulse-to-Pulse Frequency Hop: .+-.100 mc random Frequency: 5600 - 5800 mcs Pulse Train Modulation: None Delay: Each pulse delayed a controlled amount of time from the corresponding input pulse continuously from 0 - 50 us. ______________________________________
An object of the present invention is the provision of an electronic countermeasure technique. Another object of the present invention is the provision of an ECM technique which can capture the range gate of a pulse compression radar system.
Still another object of the present invention is the provision of an ECM technique which can progressively delay the range gate of an enemy radar beyond the true target pulse.
Still another object of the present invention is the provision of an ECM technique which provides that the enemy radar has no return signal within its range gate.
Yet another object of the present invention is the provision of an ECM technique which can operate against a compressive, random PRF, frequency diverse radar.